In SCIENCE, (1983) 221, pp. 661-663, MING TIEN and T. KENT KIRK have described an extracellular enzyme produced by Phanerochaete chrysosporium Burdsall, which is a basidiomycetes fungus; in the presence of hydrogen peroxide, this enzyme is capable of causing the oxidizing degradation of various model compounds having lignin substructures, as well as the degradation of fir or birch lignin.
This enzyme, called "lignin peroxidase", has been characterized [M. TIEN and T. K. KIRK, PROC. NATL. ACAD. SCI. USA, (1984) vol. 81, pp. 2280-2284] as being a glycoprotein of about 42 kDa.
French patent 2 574 427 claims two novel strains of Phanerochaete chrysosporium Burdsall which are capable of developing a particularly high ligninolytic activity in media of unlimited nitrogen content, whereas the previously known strains produced the ligninolytic enzyme only in a nitrogen-deficient culture medium, the biodegradation process which produced this enzyme also being very slow under these conditions.
According to said patent, the culture medium suitable for promoting the production of lignin peroxidase contains a source of assimilable nitrogen which can be asparagine, ammonium nitrate or ammonium tartrate; it also contains a source of assimilable carbon such as glucose, mannose, starch, melibiose, mannitol, xylose, maltose, adonitol, arabitol, fructose, sorbitol, raffinose, xylitol, D(+)-trehalose or glycerol, the last of these being preferred; it further contains a source of assimilable mineral salts such as iron citrate, KH.sub.2 PO.sub.4, ZnSO.sub.4, MnSO.sub.4, CaCl.sub.2, CuSO.sub.4, NaCl, FeSO.sub.4, CoSO.sub.4, AlK(SO.sub.4).sub.2, H.sub.3 BO.sub.3, Na.sub.2 MoO.sub.4 or MgSO.sub.4.
French patent 2 600 077 proposes significantly increasing the production yields of lignin peroxidase by cultivating the fungus Phanerochaete chrysosporium on a base culture medium supplemented with a stimulant selected from unsaturated fatty acids, natural amino acids and mixtures thereof. The preferred unsaturated fatty acids are oleic acid, linoleic acid, palmitoleic acid and arachidonic acid, preferably in emulsified form, and the preferred natural amino acids are serine, threonine, isoleucine, glycine, valine and tyrosine, but more particularly isoleucine, serine, threonine and glycine. The optimum concentration of oleic acid is about 800 mg/liter or, in the case of emulsified oleic acid, about 400 mg/liter; the optimum concentration of isoleucine is about 6.5 mg/liter.
It should be pointed out that JAGER et al. (APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Nov. 1985, pp. 1274-1278) have proposed adding a detergent, such as TWEEN 80 or TWEEN 20, to the culture medium of the fungus, in submerged cultures, in order to increase the production of lignin peroxidase in proportions comparable to that currently obtained in stationary cultures. FAISON & KIRK [APPL. ENVIRON. MICROBIOL., (1985) 49, pp. 299-304] and LEISOLA et al. [J. BIOTECHNOL., (1985) 3, pp. 97-107] have reported that the addition of veratryl alcohol, which is a secondary metabolite of Phanerochaete chrysosporium, increases the synthesis of lignin peroxidase.
In an article published in ENZ. MICROBIAL TECHNOL., (1987) 9, pp. 245-249, ASTHER et al. have shown that, in the presence of exogenous oleic acid emulsified by TWEEN 80, there is a significant increase in the production of lignin peroxidase and a considerable reduction in the fermentation time required to reach the maximum enzymic activity.
In a more recent article, published in APPL. MICROBIOL. BIOTECHNOL., (1988) 27, pp. 393-398, ASTHER et al. have reported that the production of lignin peroxidase by the fungus Phanerochaete chrysosporium is further increased when olive oil supplemented with soya azolectin, which constitutes a source of phospholipids, is added to the culture medium.
In a communication delivered at the Annual Meeting of the ASM which took place from May 8 to 13, 1988 in Miami, Fla., United States, ASTHER et al. reported that a maximum production of lignin peroxidase is obtained from cultures of Phanerochaete chrysosporium when culture is carried out at two different temperatures, namely at 37.degree. C. during the growth phase of the mycelium, for the first two days of incubation, and then at 30.degree. C. during the lignin peroxidase production phase.
LEISOLA et al. [q.v. the above-cited article published in J. BIOTECHNOL. in 1985] have identified four hemes containing lignin peroxidase activity in extracellular fluid of three-day-old cultures of Phanerochaete chrysosporium BKM-F-1767, induced by veratryl alcohol. JAGER et al. [APPL. ENVIRON. MICROBIOL., (1985) 50, pp. 1274-1278] have separated 8 peaks with an absorbance at 409 nm (hemoproteins), assuming that relatively minor differences between the profiles of the proteins simply reflect the age of the cultures.